Agriculture Reference
In-Depth Information
8.4.2.2
DROUGHT TOLERANCE
Most of the vegetables are sensitive to drought, however brinjal, cowpea,
amaranth, tomato can tolerate drought to certain extent. Genetic variabil-
ity for drought tolerance has been found in wild tomato (
S. lycopersicum)
is limited and inadequate. The best source of resistance is from other
species in the genus
Solanum
. Wild accessions of tomato i.e.
S. chees-
manii
,
S. chilense
,
S. lycopersicum
,
S. lycopersicum
var.
cerasiforme
,
S.
pennellii
,
S. peruvianum
and
S. pimpinellifolium
have stress tolerance.
S.
chilense
and
S. pennellii
produce small green fruit and have an indeter-
minate growth habit.
S chilense
is adapted to desert areas and often found
in areas where no other vegetation grows (Rick, 1973, Maldonado et al.,
2003).
S. chilense
has finely divided leaves and well-developed root sys-
tem (Sanchez-Pena, 1999).
S. chilense
has a longer primary root and more
extensive secondary root system than cultivated tomato (O'Connell et al.
2007). Drought tests show that
S. chilense
is five times more tolerant of
wilting than cultivated tomato.
S.
pennellii
has the ability to increase its
water use efficiency under drought conditions unlike the cultivated
S. ly-
copersicum
(O'Connell et al.,
2007). It has thick, round waxy leaves, is
known to produce acyl-sugars in its trichomes, and its leaves are able to
take up dew (Rick, 1973). Transfer and utilization of genes from these
drought resistant species will enhance tolerance of tomato cultivars to dry
conditions, although wide crosses with
S. pennellii
produce fertile prog-
enies,
S. chilense
is cross-incompatible with
S. lycopersicum
and embryo
rescue through tissue culture is required to produce progeny plants.
8.4.2.3
SALT TOLERANCE
Conventional breeding programs have shown very limited success in im-
provement of salt tolerance due to the genetic and physiologic complexity
of this trait (Flowers, 2004). Success in breeding for salt tolerance requires
effective screening methods, existence of genetic variability, and ability to
transfer the genes to the species of interest. Screening for salt tolerance in
the field is not a recommended practice because of the variable levels of
salinity in field soils. Screening should be done in soil-less culture with
nutrient solutions of known salt concentrations (Cuartero and Fernandez-
Munoz, 1999). Few vegetables like, beet palak, tomato can tolerate salt to
